System and method for imaging of coated substrates

ABSTRACT

The present invention relates to a system for imaging the surface of a substrate through a coating on the substrate. The system includes an infrared light source positioned to cast an infrared light upon the substrate to thereby create reflected light. A focal plane array may be positioned to receive the reflected light and generate an image therefrom. At least one optical filter may be disposed between the substrate and the focal plane array so as to pass only coating transparent wavelengths of the reflected light along an optical path between the infrared light source and the focal plane array thereby visually revealing irregular structural features of the substrate as at least one image.

STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT

[0001] The U.S. Government has a paid-up license in this invention andthe right in limited circumstances to require the patent owner tolicense to others on reasonable terms as provided for by the terms ofContract No. DACA 72-99-C-0011 awarded by SERDP.

CROSS REFERENCE TO RELATED APPLICATIONS

[0002] (Not Applicable)

BACKGROUND OF THE INVENTION

[0003] The present invention relates generally to analysis of substrateswhich are coated, and more particularly to a system and method forimaging the surface of a substrate which is coated through the coatingfor the purposes of detecting rust, pitting, corrosion, cracks,scratches, gouges, and other structural imperfections.

[0004] Aircraft components are subject to constant degradation caused byenvironmental conditions. Various agents including moisture, dust, wind,solar radiation, and air pollutants cause damage to components in theform of rust or corrosion. Although the application of a coating, suchas paint, reduces these problems substantially, it typically cannoteliminate them entirely. Moreover, other causes such as stressexperienced during flight can result in damage which a coating of paintcannot mitigate, such as stress defects and cracking. While theoccurrence of these forms of damage is to be expected, the particularrate at which any given aircraft's components degrade is highlydependent upon the particular environment of the aircraft and thecircumstances under which it operates. This is readily apparent ataircraft maintenance depots, where maintenance personnel sometimes havethe opportunity to view two aircraft of similar make and age. In manyinstances, the need for repair or replacement of components is muchgreater for one such aircraft than for the other. It is thereforeimpractical to rely upon projected maintenance schedules in determiningwhen an aircraft will need repair. The only effective way to ensure thataircraft are ready for flight is through periodic inspection.

[0005] Using traditional methods, inspection of aircraft components isaccomplished by means of visual inspection. When visually inspectingaircraft components, the coating used to protect the components becomesan obstacle because it may hide structural defects beneath. It istherefore necessary to strip the component assembly or aircraft inquestion of its paint before a proper inspection can be performed.Afterward, a new coating of paint must be applied. Obviously, thisprocess results in substantial expense in the form of labor andmaterials, and likewise requires a great amount of time. It has beenestimated that an aircraft spends twelve percent of its life in someform of maintenance or inspection, and billions of dollars are spent onaircraft maintenance every year. Apart from the inefficiency of visualinspection methods, another problem is the fact that visual inspectionis simply not as effective as might be desired. While a skillful eye maypick up most human-visible defects with a satisfactory degree ofconsistency, some defects may be very small or lie under the surface ofthe component. In many cases these defects will go unnoticed by thenaked human eye, regardless of the skill and experience of the observer.It is therefore desirable to devise a method for analyzing damage toaircraft components without the need to strip paint from the componentor rely upon the human eye alone. Some inventions offer insight into howthis problem might be solved.

[0006] One such invention is described in U.S. Pat. No. 5,426,506entitled OPTICAL METHOD AND APPARATUS FOR DETECTION OF SURFACE ANDNEAR-SUBSURFACE DEFECTS IN DENSE CERAMICS issued to Ellingson, et al.The invention described therein employs a laser of a wavelengthcalculated to penetrate the surface of an object to be analyzed. Thelaser is passed through a polarizer before being reflected by theobject, and through a second polarizer afterward. When striking theobject, that portion of light which strikes irregularities is reflectedat an altered polarity, while the portion which strikes regular featuresis reflected at its original polarity. The second polarizer isconfigured to detect this difference, and the system generates an imagereflecting it. In order to generate an image of an area, the object tobe analyzed is secured to a mount capable of translation and/or rotationand controlled by a computer or similar device. The object is movedabout under the laser beam, to thereby be scanned. The most obviousdisadvantage of this system is that in order to perform area analysis, amotorized mount typically must be used. This appears to preclude thepossibility of a hand-held unit, and the system would be highlyimpractical when applied to components or assemblies already mounted onaircraft. Another obvious disadvantage is the method is not used to seesurfaces under organic coatings and the wavelength of the laser lightwill not penetrate coatings or polymers.

[0007] A second related invention is disclosed in U.S. Pat. No.4,682,222 entitled STIMULATED SCANNING INFRARED SYSTEM issued to Smithet al. The invention uses a collimated energy beam, such as a laser, toheat an object to be analyzed. Because objects radiate infrared lightwhen they are warm, an infrared detector can then be used to detect theheat of areas of the object relative to each other. For instance,because areas which are cracked will heat at a different rate than otherareas, they can thereby be distinguished. The obvious disadvantage ofthis system is that the object to be scanned must be heated. For variousreasons, methods involving heating the object to be analyzed are notideal. For instance, a thermal shielding component of an aircraft with acoating of paint would pose a particular problem for this system. Thecomponent is specifically designed to be difficult to heat, and anysource powerful enough to heat the component would likely damage thecoating of paint. This patent additionally utilizes a technique ofthermography which does not relate to IR imaging of substrate surfacesunder organic coatings.

[0008] Still another related invention is disclosed in U.S. Pat. No.6,184,528 entitled METHOD OF SPECTRAL NONDESTRUCTIVE EVALUATION issuedto DiMarzio, et al. The invention disclosed therein employs an infraredlight source, such as an infrared laser, to cast infrared light upon asubstrate. Reflected light is measured as a function of wavelength toobtain reflectivity data. The reflectivity data of the sample substrateis compared to reflectivity data of a control substrate. Correlationsare then drawn between differences in order to determine the presence ofcorrosion. This invention achieves some of the objectives of the presentinvention, but will not detect the full range of structural featuresdetectable by the present invention and does not provide a visual imageof the substrate.

[0009] It is therefore desirable to devise a system and method foranalyzing substrates free of the aforementioned drawbacks and, further,improving upon previous systems in terms of effectiveness andresolution.

BRIEF SUMMARY OF THE INVENTION

[0010] In accordance with the present invention, there is provided asystem for imaging the surface of a substrate through a coating on thesubstrate. Coatings typically found on substrates are designed to beopaque in the visible range of the spectrum, and are often moretransparent in the infrared area of the spectrum. An infrared lightsource may be positioned to cast infrared light upon the substrate tothereby create reflected light. A focal plane array may be positioned soas to receive the reflected light and generate an image therefrom. Atleast one spectral optical filter may be disposed between the substrateand the focal plane array so as to pass only coating transparentwavelengths of the reflected light along an optical path between theinfrared light source and the focal plane array thereby visuallyrevealing structural features of the substrate as at least one image. Amultiplicity of optical filters disposed between the substrate and thefocal plane array may be employed which are operative to generate imagesin a plurality of selected wavelengths for imaging structural featuresof the substrate. A multiple imaging device may be placed intocommunication with the focal plane array for simultaneously imaging aplurality of structural features of the substrate.

[0011] Further, a computer may be employed which is combining andenhancing images generated by the system to thereby generate collectiveimages of selected structural features of the substrate. A computerprogrammed with substrate patterns for color-coding selected structuralfeatures of the substrate within the image based on the substratepatterns may be provided so as to provide visual categorization of thestructural features. Additionally, a position sensor may be employed tomark reference points on the surface of the substrate so as to storecoordinates of structural features of the substrate. A computer formedto compare images generated at selected wavelengths in a feedback loopmay be provided so as to automatically enhance image quality ofirregular selected structural features of the substrate based uponpreselected enhancement criteria. Advantageously, the infrared lightsource, the focal plane array and the at least one optical filter may becollectively formed with a hand-held device so as to be transportable byas single human operator.

[0012] The system may also include a first polarizer disposed betweenthe infrared light source and the substrate for polarizing the infraredlight to a first selected polarity. Additionally, a second polarizer maybe disposed between the substrate and the focal plane array forpolarizing the reflected light to a second selected polarity. The firstselected polarity and the second selected polarity may be oppositelyconfigured so as to prevent reflected light corresponding to regularfeatures of the substrate from being received upon the focal planearray. The polarities of the first and second polarizers may berotatable so as to selectably provide a plurality of polarities forimaging irregular structural features from the substrate.

[0013] In use, there is also provided a method for imaging the surfaceof a substrate through a coating on the substrate. The method includesdirecting infrared light upon the substrate. The infrared light may bereflected from the substrate to thereby create reflected light. Onlycoating transparent wavelengths of the reflected light may be filtered.The reflected light may be received on a focal plane array and an imagemay be generated from the focal plane array so as to visually revealirregular structural features of the substrate.

DETAILED DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 illustrates an embodiment of the system and method of thepresent invention.

[0015]FIG. 2A is a visible image of an unpainted selectively corrodedaluminum substrate on a chemical film treated (Ref. Mil-c-5541) aluminumcoupon.

[0016]FIG. 2B is an IR image of the same aluminum coupon as shown inFIG. 2A. However, in this case the substrate or aluminum coupon has beentested with 0.006″ (6 mils) of primer and top coat. The corrosivenesswas made visible under the coating by means of the system and method ofthe present invention.

[0017]FIG. 3 is an IR Image taken of a fatigue crack on a hole radiusand made visible under a coating by means of the system and method ofthe present invention.

[0018]FIG. 4 illustrates the reflectivity principles behind the presentinvention in the form of a graph illustrating sample plots ofreflectance versus wavelength for aluminum components.

DETAILED DESCRIPTION OF THE INVENTION

[0019] Referring now to the drawings wherein the showings are forpurposes of illustrating embodiments of the present invention only, andnot for purposes of limiting the same, FIG. 1 illustrates an embodimentof the system and method of the present invention. An infrared lightsource 100 is used to cast infrared light 101 in the direction of asubstrate 102 which is coated. In an embodiment of the invention, priorto reaching the substrate 102, the infrared light 101 may pass through afirst polarizer 103. The first polarizer 103 is operative to polarizethe infrared light to a first selected polarity.

[0020] Light reflected by the substrate creates reflected light 104. Inan embodiment, the reflected light 104 passes through a second polarizer105. The second polarizer 105 is operative to polarize the reflectedlight to a second selected polarity. For instance, the second polarizer105 may be configured to polarize the reflected light 104 in a directionopposite to that of first selected direction, a method known as“cross-polarity.” In this case, light of the polarity modulated by thefirst polarizer 103 will not pass through the second polarizer 105.According to basic principles of optics, the portion of the reflectedlight 104 which was reflected off of regular areas of the substrate 102will retain the polarity modulated by the first polarizer 103 andtherefore will not pass through the second polarizer 105. However, theportion of the reflected light 104 which was reflected off of irregularareas, such as corrosion or rust, will have an altered polarity and willtherefore pass through the second polarizer 105. Additionally, thispolarization technique can reduce scattering by pigments in the coatingwhich results in a clearer image of the substrate. Thus, only theportion of the reflected light 104 which was reflected off of irregularareas of the substrate 102 will pass through the second polarizer 105.The first polarizer 103 and second polarizer 105 may therefore operatein tandem to highlight the areas of the substrate 102 which areirregular because they are corroded or otherwise damaged. Additionally,the polarity modulated by the first polarizer 103 may be configured toallow viewing of the substrate 102 at various levels. This is becauselight of a polarity parallel to the substrate 102 will more easilyreflect off of the coating, while light of a polarity perpendicular tothe substrate 102 will more easily penetrate through the coating to thesubstrate beneath. Accordingly, it is possible to focus on either thesurface of the substrate itself or on the surface of the coating. Ofcourse, this methodology may be combined with the cross-polarity methoddescribed above in order to enhance particular features of the substrateat a particular level. It should be noted that although the firstpolarizer 103 and second polarizer 105 may be used in the fashiondescribed and are therefore present in a potentially preferredembodiment, they are not necessary to the function of the presentinvention, and need not be included.

[0021] Subsequent to passing through the second polarizer 105 (ifpresent), the reflected light 104 passes through an optical filter 106.The optical filter 106 is operative to filter out all except selectedwavelengths of the reflected light 104. Coatings used on, for instance,aircraft components and assemblies are generally designed to be opaquein the visible range of light. Often, they are more transparent in theinfrared range of light. Accordingly, certain wavelengths of light aremore likely to pass through the coating to be reflected by the substratebeneath. The image created by the portion of the reflected light 104having these wavelengths will represent an image primarily of thesubstrate 102 instead of the coating on the substrate. It is thereforedesirable to focus on these wavelengths to the exclusion of others, andthey become the selected wavelengths passed by the optical filter 106.The optical filter 106 need not be a single filter, but could be aseries of filters.

[0022] Subsequent to passing through the second polarizer 105 (ifpresent) and optical filter 106, the reflected light 104 reaches a focalplane 108. A focal plane array (not shown) is positioned at a focalplane 108 for the purpose of receiving an image 109 created by thereflected light 104 at the focal plane 108. Structural features of thesubstrate 102, such as cracks 110 are visible in this image 109. Thefocal plane array is operative to take this image 109 and generate it asa photograph, image on an LCD display, or otherwise represent it on ahuman-viewable medium.

[0023]FIGS. 2A, 2B, and 3 demonstrate the effectiveness of the systemand method of the present invention. FIG. 2A is a visible image of anunpainted substrate, in this case a chemical film treated (Refmil-c-5541) aluminum coupon. The structural features of the substrateare visible to the human eye. FIG. 2B is an image of the same Alodinedaluminum coupon. However, in this case the substrate has been coatedwith a 0.006″ thickness (6 mils) of primer and a top coat. Thestructural features of the substrate are only visible because this imagewas generated using the system and method of the present invention. FIG.3 is an image of a fastener hole, with a crack in it made visible bymeans of the system and method of the present invention. Experimentsproved detectability of cracks as small as 0.030″ in length and pits assmall as 0.001″ in diameter.

[0024]FIG. 4 illustrates the reflectivity principles behind the presentinvention in the form of a graph illustrating sample plots ofreflectance versus wavelength for aluminum components. The first plot400 is for an uncorroded aluminum component with a layer of primer andpaint having a total thickness of 0.0037″ (3.7 mils). The second plot401 is for a corroded aluminum component with the same layer of paintand primer. By comparing the plots 400 and 401 a difference will be seenbetween the two plots 400 and 401 in the area between approximately awave length of 3.5 microns (higher reflectance) and a wave length of 5.5microns, with a dip at approximately a wave length of 4.4 microns. Thefirst plot 400 is stronger than the second plot 401 because theuncorroded aluminum reflects a higher portion of the infrared lightpassing through the paint than the corroded aluminum does.

[0025] The above describes a basic implementation of the presentinvention. The invention may take a variety of embodiments designed toprovide additional features. For instance, dependent upon the coatingused on the substrate or upon the particular structural features inwhich an operator has interest, it may be expedient to view thesubstrate in a variety of wavelengths. The system may therefore includea multiplicity of optical filters which may be manually or automaticallychangeable in order to accomplish this objective. Likewise, the polarityof the polarizers may be rotatable in order to provide imaging of thesubstrate in a variety of combinations of polarities. As an additionalmodification, the provision of imaging at a variety of wavelengthsand/or combinations of polarities could be accomplished by means of amultiple imaging device. This would allow the system to create aplurality of images simultaneously for rapid processing. In thisrespect, the multiple imaging device could process and generate imagesat several different wavelengths and polarities.

[0026] Following the above line of additions, the system could include acomputer for processing the images provided by the system in order toprovide improved images of selected irregular structural features of thesubstrate. As will be recognized by those in the art, a given structuralfeature of the substrate will be more readily observable in certainwavelengths and/or combinations of polarities than in others. Thecomputer could contain a database of information with respect to whichcombinations were effective for viewing, for instance, corrosion. Theoperator would then simply indicate to the computer that he desired toview corrosion, and the computer would automatically select thecombination or combinations appropriate to so doing. Additionally,images or signal taken in the IR from the surface or internal to thecoating may be substrated out as background signals to enhance imagestaken on the substrate to be inspected for an improved composite imageof the substrate surface.

[0027] The computer could additionally be programmed to recognizeselected structural features of the substrate. As will be apparent tothose in the art, this can be accomplished by means of softwareoperative to search for substrate patterns. Such substrate patterns mayinclude specific corrosion characteristics, extrusions and inclusions ofthe surface and other characteristics which indicates that the substrateis damaged in some manner. Once identified, the features could belabeled for the user. For instance, the computer could providecolor-coded images of the substrate. The color-coding could operate as afunction of feature type or level of structural integrity. In the formercase, the computer could assign, for instance, red to corrosion andblack to cracking. In the later case, the computer could assign, forinstance, red to undamaged portions of the substrate, yellow tomoderately damaged portions of the substrate, and blue to seriouslydamaged portions of the substrate. In any event, the computer operatesto perform a preliminary analysis which may be useful to the operator.

[0028] The system could incorporate an automatic feedback loop driven byhardware or software, operative to rapidly find the best combinations ofwavelengths and/or polarities for viewing the substrate, or selectedstructural features of the substrate. The computer would experiment withvarious combinations and use the above mentioned identificationtechniques in order to determine which combinations were working mosteffectively. It could then rapidly determine which combination orcombinations were most appropriate for the task at hand, andautomatically employ those combinations.

[0029] Furthermore, the system could comprise an automatic pointerdevice operative to generate an alarm or automatic notification whenselected structural features are observed. This could take the form ofsoftware operative to impose a crosshair on the image or software orhardware operative to automatically zoom on selected structural featuresof the image, for instance. The latter would be highly useful inapplications where it is necessary to analyze large objects forpotentially subtle signs of damage. The operator could move the view ofthe system over the object and, when the system detected a defect ofbelow a preset visibility threshold, it would automatically zoom in onthe defect in question to ensure identification of the defect.

[0030] In further keeping with the above line of improvements, aposition sensor could be included in order to store coordinates on thesubstrate for future reference. The coordinates could be identified, forinstance, with respect to a reference point on the substrate. In thisexample, the position sensor could record the coordinates of the systemon the substrate as a function of distance to and direction from thereference point. Marking by the position sensor could be accomplishedautomatically by a computer, or could be performable by the operator.

[0031] Still a further embodiment of the invention would provide acommunications device, such as a communications port or transmitter,operative to put the system in communication with an external device ornetwork. Including a communications device could enhance the usefulnessof the system in many ways. For instance, an external computer couldcontain a database of coatings available on the market. In order toinspect the substrate, the operator would first identify its coating andsend a query to the external computer. The external computer could thenprovide the system with information as to which combination ofwavelengths and/or polarities was appropriate in order to effectivelyview the substrate. A further improvement would use the system's ownimaging system to automatically assess features of the coating and sendvalues with respect to these features to the external computer. Theexternal computer could compare these values to values in its owndatabase and identify the coating itself before sending the relevantdata. This would eliminate the need of the operator to identify thecoating in question.

[0032] Another use of communications capability would be to allow anoperator to call up remotely stored control images. The control imagescould be either images of an undamaged substrate of the same design orthe same substrate at an earlier time. The control image could bedisplayed on the same screen as the image then being generated in orderto allow convenient comparison by the operator. The generated imagecould additionally be compared to the control image by hardware orsoftware operative to identify discrepancies, in order to furtherclarify which structural features of the substrate were irregular. Thislatter method would be particularly helpful in situations in which thesubstrate has, in its undamaged form, peculiar features which mayotherwise appear to be damage. The computer could use the control imageas a mask to eliminate all structural features expected to be in thesubstrate in order to ensure that physically irregular but appropriatefeatures were not identified as damage.

[0033] It will additionally be apparent to those in the art that theimages generated by use of the system and method of the presentinvention may be further operated upon in order to provide additionalinformation. For instance, a database could be established for thepurpose of storing images taken of a given substrate over time. Theimages so stored could be compared, for instance by a computer, in orderto assess the rate at which damage was occurring to the substrate. Theapproximate time at which the substrate would become unsuitable for usecould therefore be extrapolated, and projected repair and maintenanceschedules developed.

[0034] Still a further embodiment of the invention would use theinfrared light source to cause the substrate to emit light. This couldbe more easily accomplished if the infrared light source were a laser.Certain structural features of the substrate will have differentchemical compositions than the undamaged portion of the substrate. Theywill therefore emit light of different wavelengths than the undamagedportion of the substrate. The system could therefore be configured toview, for instance, corrosion by means of selecting the selectedwavelengths with respect to the wavelength of light emitted by corrosionon the substrate. A filtered IR light source (spectral/polarized) couldalso be used in the embodiment as just described.

[0035] Obviously, any of the above described features could be combined.For instance, the aforementioned damage-over-time analysis methoddescribed would be particularly useful in combination with a positionsensor as described further above. Additionally, while the presentinvention has been described in connection with inspection of substratesfor damage, it is understood that the invention may be employed in avariety of applications. For instance, the present invention could beused to read serial codes or other identifying marks on substrates.

[0036] Additional modifications and improvements of the presentinvention may also be apparent to those of ordinary skill in the art.Thus, the particular combination of elements described and illustratedherein is intended to represent only certain embodiments of the presentinvention, and is not intended to serve a limitation on systems andmethods within the spirit and scope of the invention.

What is claimed is:
 1. A system for imaging the surface of a substratethrough a coating on the substrate, comprising: a. an infrared lightsource positioned to cast infrared light upon the substrate to therebycreate reflected light; b. a focal plane array positioned to receive thereflected light off the substrate surface and generating an imagetherefrom; and c. at least one spectral optical filter disposed betweenthe substrate and the focal plane array so as to pass only coatingtransparent wavelengths of the reflected light along an optical pathbetween the infrared light source and the focal plane array therebyvisually revealing structural features of the substrate as at least oneimage.
 2. The system of claim 1, further comprising a multiplicity ofoptical filters disposed between the substrate and the focal plane arrayfor generating images in a plurality of selected wavelengths and forimaging structural features of the substrate.
 3. The system of claim 1,further comprising a multiple imaging device in communication with thefocal plane array for simultaneously imaging a plurality of structuralfeatures of the substrate.
 4. The system of claim 1, further comprisinga computer combining and enhancing images generated by the system tothereby generate collective images of selected structural features ofthe substrate.
 5. The system of claim 1, further comprising a computerprogrammed with substrate patterns for color-coding selected structuralfeatures of the substrate within the image based on the substratepatterns so as to provide visual categorization of the structuralfeatures.
 6. The system of claim 1, further comprising a position sensorfor marking reference points on the surface of the substrate so as tostore coordinates of structural features of the substrate.
 7. The systemof claim 1, further comprising a computer comparing images generated atselected wavelengths in a feedback loop so as to automatically enhanceimage quality of selected structural features of the substrate basedupon preselected enhancement criteria.
 8. The system of claim 1, whereinthe infrared light source, the focal plane array and the at least oneoptical filter are collectively formed within a hand-held devicetransportable by a single human operator.
 9. The system of claim 1,further comprising: a. a first polarizer disposed between the infraredlight source and the substrate for polarizing the infrared light to afirst selected polarity; and b. a second polarizer disposed between thesubstrate and the focal plane array for polarizing the reflected lightto a second selected polarity.
 10. The system of claim 9, wherein thefirst selected polarity and second selected polarity are oppositelyconfigured so as to prevent reflected light corresponding to selectedstructural features of the substrate from being received upon the focalplane array.
 11. The system of claim 9, further comprising amultiplicity of optical filters providing imaging at a plurality ofselected wavelengths so as to form an image of a plurality of structuralfeatures from the substrate.
 12. The system of claim 9, wherein thepolarities of the first and second polarizers are rotatable so as toselectably provide a plurality of polarities for imaging structuralfeatures from the substrate.
 13. The system of claim 9, furthercomprising a multiple imaging device in communication with the focalplane array for simultaneously imaging a plurality of structuralfeatures of the substrate.
 14. The system of claim 9, further comprisinga computer combining and enhancing images generated by the system tothereby generate collective images of selected structural features ofthe substrate.
 15. The system of claim 9, further comprising a computerprogrammed with substrate patterns for color-coding selected structuralfeatures of the substrate within the image based on the substratepatterns so as to provide visual categorization of the irregularstructural features.
 16. The system of claim 9, further comprising aposition sensor for marking reference points on the surface of thesubstrate so as to store coordinates of structural features of thesubstrate.
 17. The system of claim 9, further comprising a computercomparing a plurality of selected wavelengths and selected polarities ina feedback loop so as to automatically enhance the image quality ofselected structural features of the substrate based upon selectedcriteria.
 18. The system of claim 9, wherein the infrared light source,the focal plane array and the at least one optical filter arecollectively formed within a hand-held device transportable by a singlehuman operator.
 19. The system of claim 1, further comprising acommunication device for transferring the revealed structural featuresto a remote human viewable medium.
 20. A method for imaging the surfaceof a substrate through a coating on the substrate, comprising: a.directing infrared light upon the substrate; b. reflecting the infraredlight from the substrate to thereby create reflected light; c. filteringonly coating transparent wavelengths of the reflected light; d.receiving the reflected light on a focal plane array; and e. generatingat least one image from the focal plane array so as to visually revealstructural features of the substrate.
 21. The method of claim 19,further comprising comparing a plurality of images generated upon thefocal plane array as a function of time to thereby establish a rate ofdegradation for the substrate.
 22. The method of claim 20, furthercomprising selecting the selected wavelengths and first and secondselected polarities from a database storing reflectivity characteristicsof coatings found on substrates.
 23. The method of claim 20, furthercomprising comparing the generated image with a pre-selected controlimage to thereby identify irregular structural features of thesubstrate.
 24. The method of claim 20, further comprising: a. directingthe infrared light through a first polarizer before the infrared lightreaches the substrate so as to polarize the infrared light to a firstselected polarity; b. directing the reflected light through a secondpolarizer before the infrared light reaches the focal plane array so asto polarize the reflected to a second selected polarity;
 25. The methodof claim 24, wherein the first selected polarity and second selectedpolarity are oppositely configured so as to prevent reflected lightcorresponding to selected structural features of the substrate frombeing received upon the focal plane array.
 26. The method of claim 24,further comprising comparing a plurality of images generated upon thefocal plane array as a function of time to thereby establish a rate ofdegradation for the substrate.
 27. The method of claim 24, furthercomprising selecting the selected wavelengths and first and secondselected polarities from a database storing reflectivity characteristicsof coatings found on substrates.
 28. The method of claim 24, furthercomprising comparing the generated image with a pre-selected controlimage to thereby identify irregular structural features of thesubstrate.
 29. The method of claim 20, further comprising transferringthe generated image to a remote human-viewable medium.